add triggered streaming write to dl-streaming-101

[newfront]

finally wrapping up the intro content. Just need to do some minor additions

1. Create the Rate Limited, Interval Limited (triggered) DL table to DL table example app from ecomm_by_day
2. Show streamingQuery.latestProgress - minor comments on the batch identifier (microbatch), etc
3. Moving on to Moving Fast and Moving Slow - since it requires triggers, limits to not fall over.